Abstract: In this paper, the effect of different amounts of 75 FeSi and Re-Si-Fe alloy, added to molten iron, on the properties of high strength gray iron is studied. The experimental results obtained show that the addition of a Re inoculant could reduce the undercooling, HB, of the cast iron and its tendency to form primary iron carbides and blowhole; and increase its tensile strength. Based on the research findings, a new type of Re-Si-Fe alloy inoculant is prepared for molten iron. The machine tool castings containing such inoculant have satisfactory properties.